1. Field of the Invention
The present invention relates to an ultrasound diagnostic imaging apparatus and an ultrasound diagnostic imaging method.
2. Description of Related Art
Conventionally, ultrasound diagnostic imaging apparatuses including ultrasound probes with a plurality of transducers aligned therein are known. Such ultrasound diagnostic imaging apparatuses perform transmission and reception of ultrasound waves with respect to a subject such as a living body, generate ultrasound image data according to signals obtained from the received ultrasound waves and display ultrasound images in the image display apparatuses based on the generated ultrasound image data. Ultrasound diagnosis using such apparatuses can be repeatedly performed because real time subject conditions such as heart beat and fetus movement can be obtained with simple operation by touching the body surface of a subject with an ultrasound probe and such operation is noninvasive and safe.
However, images obtained by these ultrasound diagnostic imaging apparatuses includes various noises and speckles that occur due to interference of the receive signals obtained from the ultrasound waves in addition to information relating to tissues in subjects. These noises and speckles become obstacles for correctly grasping the position and shapes at the borders of tissues in subjects.
In recent years, as a processing method for reducing the noises and speckles, for example, a spatial compounding method is suggested in JP 2011-78792 and JP 2011-125690. In the spatial compounding method, transmitting and receiving of ultrasound waves are performed in a plurality of different directions at the same time with respect to the same part in a subject and average weighting is performed with respect to the obtained plurality of ultrasound image data sets. In such way, for example, in a case where N sheets of ultrasound image data sets are obtained, noises and speckles are reduced by the square root of N in the synthetic image formed by the N sheets of ultrasound image data sets being synthesized.
Moreover, according to the spatial compounding method, visibility of specular interfaces can be improved. That is, for example, with respect to a curved interface between a soft tissue and a bone, a strong reflection ultrasound waves can be obtained when the direction of the ultrasound beam formed of the transmission ultrasound waves is strictly at a right angle. However, the intensity of the reflection ultrasound waves can be greatly reduced just by the direction of the ultrasound beam shifting by few degrees from the right angle with respect to the interface. Often times, the interfaces between soft tissues and bones are curved, and therefore, only parts of such curved interfaces can be visualized clearly when ultrasound scanning is performed only in one direction as in the conventional methods. However, according to the spatial compounding method, interface images can be obtained from a plurality of different angles and curved interfaces can be visualized continuously for a greater view.